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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="SQL-SYNTAX-LEXICAL"
>4.1. Lexical Structure</A
></H1
><P
>   SQL input consists of a sequence of
   <I
CLASS="FIRSTTERM"
>commands</I
>.  A command is composed of a
   sequence of <I
CLASS="FIRSTTERM"
>tokens</I
>, terminated by a
   semicolon (<SPAN
CLASS="QUOTE"
>";"</SPAN
>).  The end of the input stream also
   terminates a command.  Which tokens are valid depends on the syntax
   of the particular command.
  </P
><P
>   A token can be a <I
CLASS="FIRSTTERM"
>key word</I
>, an
   <I
CLASS="FIRSTTERM"
>identifier</I
>, a <I
CLASS="FIRSTTERM"
>quoted
   identifier</I
>, a <I
CLASS="FIRSTTERM"
>literal</I
> (or
   constant), or a special character symbol.  Tokens are normally
   separated by whitespace (space, tab, newline), but need not be if
   there is no ambiguity (which is generally only the case if a
   special character is adjacent to some other token type).
  </P
><P
>    For example, the following is (syntactically) valid SQL input:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT * FROM MY_TABLE;
UPDATE MY_TABLE SET A = 5;
INSERT INTO MY_TABLE VALUES (3, 'hi there');</PRE
><P>
    This is a sequence of three commands, one per line (although this
    is not required; more than one command can be on a line, and
    commands can usefully be split across lines).
   </P
><P
>   Additionally, <I
CLASS="FIRSTTERM"
>comments</I
> can occur in SQL
   input.  They are not tokens, they are effectively equivalent to
   whitespace.
  </P
><P
>   The SQL syntax is not very consistent regarding what tokens
   identify commands and which are operands or parameters.  The first
   few tokens are generally the command name, so in the above example
   we would usually speak of a <SPAN
CLASS="QUOTE"
>"SELECT"</SPAN
>, an
   <SPAN
CLASS="QUOTE"
>"UPDATE"</SPAN
>, and an <SPAN
CLASS="QUOTE"
>"INSERT"</SPAN
> command.  But
   for instance the <TT
CLASS="COMMAND"
>UPDATE</TT
> command always requires
   a <TT
CLASS="TOKEN"
>SET</TT
> token to appear in a certain position, and
   this particular variation of <TT
CLASS="COMMAND"
>INSERT</TT
> also
   requires a <TT
CLASS="TOKEN"
>VALUES</TT
> in order to be complete.  The
   precise syntax rules for each command are described in <A
HREF="reference.html"
>Part VI</A
>.
  </P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-IDENTIFIERS"
>4.1.1. Identifiers and Key Words</A
></H2
><P
>    Tokens such as <TT
CLASS="TOKEN"
>SELECT</TT
>, <TT
CLASS="TOKEN"
>UPDATE</TT
>, or
    <TT
CLASS="TOKEN"
>VALUES</TT
> in the example above are examples of
    <I
CLASS="FIRSTTERM"
>key words</I
>, that is, words that have a fixed
    meaning in the SQL language.  The tokens <TT
CLASS="TOKEN"
>MY_TABLE</TT
>
    and <TT
CLASS="TOKEN"
>A</TT
> are examples of
    <I
CLASS="FIRSTTERM"
>identifiers</I
>.  They identify names of
    tables, columns, or other database objects, depending on the
    command they are used in.  Therefore they are sometimes simply
    called <SPAN
CLASS="QUOTE"
>"names"</SPAN
>.  Key words and identifiers have the
    same lexical structure, meaning that one cannot know whether a
    token is an identifier or a key word without knowing the language.
    A complete list of key words can be found in <A
HREF="sql-keywords-appendix.html"
>Appendix C</A
>.
   </P
><P
>    SQL identifiers and key words must begin with a letter
    (<TT
CLASS="LITERAL"
>a</TT
>-<TT
CLASS="LITERAL"
>z</TT
>, but also letters with
    diacritical marks and non-Latin letters) or an underscore
    (<TT
CLASS="LITERAL"
>_</TT
>).  Subsequent characters in an identifier or
    key word can be letters, underscores, digits
    (<TT
CLASS="LITERAL"
>0</TT
>-<TT
CLASS="LITERAL"
>9</TT
>), or dollar signs
    (<TT
CLASS="LITERAL"
>$</TT
>).  Note that dollar signs are not allowed in identifiers
    according to the letter of the SQL standard, so their use might render
    applications less portable.
    The SQL standard will not define a key word that contains
    digits or starts or ends with an underscore, so identifiers of this
    form are safe against possible conflict with future extensions of the
    standard.
   </P
><P
>    
    The system uses no more than <TT
CLASS="SYMBOL"
>NAMEDATALEN</TT
>-1
    bytes of an identifier; longer names can be written in
    commands, but they will be truncated.  By default,
    <TT
CLASS="SYMBOL"
>NAMEDATALEN</TT
> is 64 so the maximum identifier
    length is 63 bytes. If this limit is problematic, it can be raised by
    changing the <TT
CLASS="SYMBOL"
>NAMEDATALEN</TT
> constant in
    <TT
CLASS="FILENAME"
>src/include/pg_config_manual.h</TT
>.
   </P
><P
>    
    Key words and unquoted identifiers are case insensitive.  Therefore:
</P><PRE
CLASS="PROGRAMLISTING"
>UPDATE MY_TABLE SET A = 5;</PRE
><P>
    can equivalently be written as:
</P><PRE
CLASS="PROGRAMLISTING"
>uPDaTE my_TabLE SeT a = 5;</PRE
><P>
    A convention often used is to write key words in upper
    case and names in lower case, e.g.:
</P><PRE
CLASS="PROGRAMLISTING"
>UPDATE my_table SET a = 5;</PRE
><P>
   </P
><P
>    
    There is a second kind of identifier:  the <I
CLASS="FIRSTTERM"
>delimited
    identifier</I
> or <I
CLASS="FIRSTTERM"
>quoted
    identifier</I
>.  It is formed by enclosing an arbitrary
    sequence of characters in double-quotes
    (<TT
CLASS="LITERAL"
>"</TT
>).  A delimited
    identifier is always an identifier, never a key word.  So
    <TT
CLASS="LITERAL"
>"select"</TT
> could be used to refer to a column or
    table named <SPAN
CLASS="QUOTE"
>"select"</SPAN
>, whereas an unquoted
    <TT
CLASS="LITERAL"
>select</TT
> would be taken as a key word and
    would therefore provoke a parse error when used where a table or
    column name is expected.  The example can be written with quoted
    identifiers like this:
</P><PRE
CLASS="PROGRAMLISTING"
>UPDATE "my_table" SET "a" = 5;</PRE
><P>
   </P
><P
>    Quoted identifiers can contain any character, except the character
    with code zero.  (To include a double quote, write two double quotes.)
    This allows constructing table or column names that would
    otherwise not be possible, such as ones containing spaces or
    ampersands.  The length limitation still applies.
   </P
><P
>    A variant of quoted
    identifiers allows including escaped Unicode characters identified
    by their code points.  This variant starts
    with <TT
CLASS="LITERAL"
>U&amp;</TT
> (upper or lower case U followed by
    ampersand) immediately before the opening double quote, without
    any spaces in between, for example <TT
CLASS="LITERAL"
>U&amp;"foo"</TT
>.
    (Note that this creates an ambiguity with the
    operator <TT
CLASS="LITERAL"
>&amp;</TT
>.  Use spaces around the operator to
    avoid this problem.)  Inside the quotes, Unicode characters can be
    specified in escaped form by writing a backslash followed by the
    four-digit hexadecimal code point number or alternatively a
    backslash followed by a plus sign followed by a six-digit
    hexadecimal code point number.  For example, the
    identifier <TT
CLASS="LITERAL"
>"data"</TT
> could be written as
</P><PRE
CLASS="PROGRAMLISTING"
>U&amp;"d\0061t\+000061"</PRE
><P>
    The following less trivial example writes the Russian
    word <SPAN
CLASS="QUOTE"
>"slon"</SPAN
> (elephant) in Cyrillic letters:
</P><PRE
CLASS="PROGRAMLISTING"
>U&amp;"\0441\043B\043E\043D"</PRE
><P>
   </P
><P
>    If a different escape character than backslash is desired, it can
    be specified using
    the <TT
CLASS="LITERAL"
>UESCAPE</TT
>
    clause after the string, for example:
</P><PRE
CLASS="PROGRAMLISTING"
>U&amp;"d!0061t!+000061" UESCAPE '!'</PRE
><P>
    The escape character can be any single character other than a
    hexadecimal digit, the plus sign, a single quote, a double quote,
    or a whitespace character.  Note that the escape character is
    written in single quotes, not double quotes.
   </P
><P
>    To include the escape character in the identifier literally, write
    it twice.
   </P
><P
>    The Unicode escape syntax works only when the server encoding is
    <TT
CLASS="LITERAL"
>UTF8</TT
>.  When other server encodings are used, only code
    points in the ASCII range (up to <TT
CLASS="LITERAL"
>\007F</TT
>) can be
    specified.  Both the 4-digit and the 6-digit form can be used to
    specify UTF-16 surrogate pairs to compose characters with code
    points larger than U+FFFF, although the availability of the
    6-digit form technically makes this unnecessary.  (Surrogate
    pairs are not stored directly, but combined into a single
    code point that is then encoded in UTF-8.)
   </P
><P
>    Quoting an identifier also makes it case-sensitive, whereas
    unquoted names are always folded to lower case.  For example, the
    identifiers <TT
CLASS="LITERAL"
>FOO</TT
>, <TT
CLASS="LITERAL"
>foo</TT
>, and
    <TT
CLASS="LITERAL"
>"foo"</TT
> are considered the same by
    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, but
    <TT
CLASS="LITERAL"
>"Foo"</TT
> and <TT
CLASS="LITERAL"
>"FOO"</TT
> are
    different from these three and each other.  (The folding of
    unquoted names to lower case in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is
    incompatible with the SQL standard, which says that unquoted names
    should be folded to upper case.  Thus, <TT
CLASS="LITERAL"
>foo</TT
>
    should be equivalent to <TT
CLASS="LITERAL"
>"FOO"</TT
> not
    <TT
CLASS="LITERAL"
>"foo"</TT
> according to the standard.  If you want
    to write portable applications you are advised to always quote a
    particular name or never quote it.)
   </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-CONSTANTS"
>4.1.2. Constants</A
></H2
><P
>    There are three kinds of <I
CLASS="FIRSTTERM"
>implicitly-typed
    constants</I
> in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>:
    strings, bit strings, and numbers.
    Constants can also be specified with explicit types, which can
    enable more accurate representation and more efficient handling by
    the system. These alternatives are discussed in the following
    subsections.
   </P
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-STRINGS"
>4.1.2.1. String Constants</A
></H3
><P
>     
     A string constant in SQL is an arbitrary sequence of characters
     bounded by single quotes (<TT
CLASS="LITERAL"
>'</TT
>), for example
     <TT
CLASS="LITERAL"
>'This is a string'</TT
>.  To include
     a single-quote character within a string constant,
     write two adjacent single quotes, e.g.,
     <TT
CLASS="LITERAL"
>'Dianne''s horse'</TT
>.
     Note that this is <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> the same as a double-quote
     character (<TT
CLASS="LITERAL"
>"</TT
>). 
    </P
><P
>     Two string constants that are only separated by whitespace
     <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>with at least one newline</I
></SPAN
> are concatenated
     and effectively treated as if the string had been written as one
     constant.  For example:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 'foo'
'bar';</PRE
><P>
     is equivalent to:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 'foobar';</PRE
><P>
     but:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 'foo'      'bar';</PRE
><P>
     is not valid syntax.  (This slightly bizarre behavior is specified
     by <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>; <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is
     following the standard.)
    </P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-STRINGS-ESCAPE"
>4.1.2.2. String Constants with C-style Escapes</A
></H3
><P
>     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> also accepts <SPAN
CLASS="QUOTE"
>"escape"</SPAN
>
     string constants, which are an extension to the SQL standard.
     An escape string constant is specified by writing the letter
     <TT
CLASS="LITERAL"
>E</TT
> (upper or lower case) just before the opening single
     quote, e.g., <TT
CLASS="LITERAL"
>E'foo'</TT
>.  (When continuing an escape string
     constant across lines, write <TT
CLASS="LITERAL"
>E</TT
> only before the first opening
     quote.)
     Within an escape string, a backslash character (<TT
CLASS="LITERAL"
>\</TT
>) begins a
     C-like <I
CLASS="FIRSTTERM"
>backslash escape</I
> sequence, in which the combination
     of backslash and following character(s) represent a special byte
     value, as shown in <A
HREF="sql-syntax-lexical.html#SQL-BACKSLASH-TABLE"
>Table 4-1</A
>.
    </P
><DIV
CLASS="TABLE"
><A
NAME="SQL-BACKSLASH-TABLE"
></A
><P
><B
>Table 4-1. Backslash Escape Sequences</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><THEAD
><TR
><TH
>Backslash Escape Sequence</TH
><TH
>Interpretation</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>\b</TT
></TD
><TD
>backspace</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>\f</TT
></TD
><TD
>form feed</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>\n</TT
></TD
><TD
>newline</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>\r</TT
></TD
><TD
>carriage return</TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>\t</TT
></TD
><TD
>tab</TD
></TR
><TR
><TD
>         <TT
CLASS="LITERAL"
>\<TT
CLASS="REPLACEABLE"
><I
>o</I
></TT
></TT
>,
         <TT
CLASS="LITERAL"
>\<TT
CLASS="REPLACEABLE"
><I
>oo</I
></TT
></TT
>,
         <TT
CLASS="LITERAL"
>\<TT
CLASS="REPLACEABLE"
><I
>ooo</I
></TT
></TT
>
         (<TT
CLASS="REPLACEABLE"
><I
>o</I
></TT
> = 0 - 7)
        </TD
><TD
>octal byte value</TD
></TR
><TR
><TD
>         <TT
CLASS="LITERAL"
>\x<TT
CLASS="REPLACEABLE"
><I
>h</I
></TT
></TT
>,
         <TT
CLASS="LITERAL"
>\x<TT
CLASS="REPLACEABLE"
><I
>hh</I
></TT
></TT
>
         (<TT
CLASS="REPLACEABLE"
><I
>h</I
></TT
> = 0 - 9, A - F)
        </TD
><TD
>hexadecimal byte value</TD
></TR
><TR
><TD
>         <TT
CLASS="LITERAL"
>\u<TT
CLASS="REPLACEABLE"
><I
>xxxx</I
></TT
></TT
>,
         <TT
CLASS="LITERAL"
>\U<TT
CLASS="REPLACEABLE"
><I
>xxxxxxxx</I
></TT
></TT
>
         (<TT
CLASS="REPLACEABLE"
><I
>x</I
></TT
> = 0 - 9, A - F)
        </TD
><TD
>16 or 32-bit hexadecimal Unicode character value</TD
></TR
></TBODY
></TABLE
></DIV
><P
>     Any other
     character following a backslash is taken literally. Thus, to
     include a backslash character, write two backslashes (<TT
CLASS="LITERAL"
>\\</TT
>).
     Also, a single quote can be included in an escape string by writing
     <TT
CLASS="LITERAL"
>\'</TT
>, in addition to the normal way of <TT
CLASS="LITERAL"
>''</TT
>.
    </P
><P
>     It is your responsibility that the byte sequences you create,
     especially when using the octal or hexadecimal escapes, compose
     valid characters in the server character set encoding.  When the
     server encoding is UTF-8, then the Unicode escapes or the
     alternative Unicode escape syntax, explained
     in <A
HREF="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS-UESCAPE"
>Section 4.1.2.3</A
>, should be used
     instead.  (The alternative would be doing the UTF-8 encoding by
     hand and writing out the bytes, which would be very cumbersome.)
    </P
><P
>     The Unicode escape syntax works fully only when the server
     encoding is <TT
CLASS="LITERAL"
>UTF8</TT
>.  When other server encodings are
     used, only code points in the ASCII range (up
     to <TT
CLASS="LITERAL"
>\u007F</TT
>) can be specified.  Both the 4-digit and
     the 8-digit form can be used to specify UTF-16 surrogate pairs to
     compose characters with code points larger than U+FFFF, although
     the availability of the 8-digit form technically makes this
     unnecessary.  (When surrogate pairs are used when the server
     encoding is <TT
CLASS="LITERAL"
>UTF8</TT
>, they are first combined into a
     single code point that is then encoded in UTF-8.)
    </P
><DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
>     If the configuration parameter
     <A
HREF="runtime-config-compatible.html#GUC-STANDARD-CONFORMING-STRINGS"
>standard_conforming_strings</A
> is <TT
CLASS="LITERAL"
>off</TT
>,
     then <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> recognizes backslash escapes
     in both regular and escape string constants.  However, as of
     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 9.1, the default is <TT
CLASS="LITERAL"
>on</TT
>, meaning
     that backslash escapes are recognized only in escape string constants.
     This behavior is more standards-compliant, but might break applications
     which rely on the historical behavior, where backslash escapes
     were always recognized.  As a workaround, you can set this parameter
     to <TT
CLASS="LITERAL"
>off</TT
>, but it is better to migrate away from using backslash
     escapes.  If you need to use a backslash escape to represent a special
     character, write the string constant with an <TT
CLASS="LITERAL"
>E</TT
>.
    </P
><P
>     In addition to <TT
CLASS="VARNAME"
>standard_conforming_strings</TT
>, the configuration
     parameters <A
HREF="runtime-config-compatible.html#GUC-ESCAPE-STRING-WARNING"
>escape_string_warning</A
> and
     <A
HREF="runtime-config-compatible.html#GUC-BACKSLASH-QUOTE"
>backslash_quote</A
> govern treatment of backslashes
     in string constants.
    </P
></TD
></TR
></TABLE
></DIV
><P
>     The character with the code zero cannot be in a string constant.
    </P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-STRINGS-UESCAPE"
>4.1.2.3. String Constants with Unicode Escapes</A
></H3
><P
>     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> also supports another type
     of escape syntax for strings that allows specifying arbitrary
     Unicode characters by code point.  A Unicode escape string
     constant starts with <TT
CLASS="LITERAL"
>U&amp;</TT
> (upper or lower case
     letter U followed by ampersand) immediately before the opening
     quote, without any spaces in between, for
     example <TT
CLASS="LITERAL"
>U&amp;'foo'</TT
>.  (Note that this creates an
     ambiguity with the operator <TT
CLASS="LITERAL"
>&amp;</TT
>.  Use spaces
     around the operator to avoid this problem.)  Inside the quotes,
     Unicode characters can be specified in escaped form by writing a
     backslash followed by the four-digit hexadecimal code point
     number or alternatively a backslash followed by a plus sign
     followed by a six-digit hexadecimal code point number.  For
     example, the string <TT
CLASS="LITERAL"
>'data'</TT
> could be written as
</P><PRE
CLASS="PROGRAMLISTING"
>U&amp;'d\0061t\+000061'</PRE
><P>
     The following less trivial example writes the Russian
     word <SPAN
CLASS="QUOTE"
>"slon"</SPAN
> (elephant) in Cyrillic letters:
</P><PRE
CLASS="PROGRAMLISTING"
>U&amp;'\0441\043B\043E\043D'</PRE
><P>
    </P
><P
>     If a different escape character than backslash is desired, it can
     be specified using
     the <TT
CLASS="LITERAL"
>UESCAPE</TT
>
     clause after the string, for example:
</P><PRE
CLASS="PROGRAMLISTING"
>U&amp;'d!0061t!+000061' UESCAPE '!'</PRE
><P>
     The escape character can be any single character other than a
     hexadecimal digit, the plus sign, a single quote, a double quote,
     or a whitespace character.
    </P
><P
>     The Unicode escape syntax works only when the server encoding is
     <TT
CLASS="LITERAL"
>UTF8</TT
>.  When other server encodings are used, only
     code points in the ASCII range (up to <TT
CLASS="LITERAL"
>\007F</TT
>)
     can be specified.  Both the 4-digit and the 6-digit form can be
     used to specify UTF-16 surrogate pairs to compose characters with
     code points larger than U+FFFF, although the availability of the
     6-digit form technically makes this unnecessary.  (When surrogate
     pairs are used when the server encoding is <TT
CLASS="LITERAL"
>UTF8</TT
>, they
     are first combined into a single code point that is then encoded
     in UTF-8.)
    </P
><P
>     Also, the Unicode escape syntax for string constants only works
     when the configuration
     parameter <A
HREF="runtime-config-compatible.html#GUC-STANDARD-CONFORMING-STRINGS"
>standard_conforming_strings</A
> is
     turned on.  This is because otherwise this syntax could confuse
     clients that parse the SQL statements to the point that it could
     lead to SQL injections and similar security issues.  If the
     parameter is set to off, this syntax will be rejected with an
     error message.
    </P
><P
>     To include the escape character in the string literally, write it
     twice.
    </P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-DOLLAR-QUOTING"
>4.1.2.4. Dollar-quoted String Constants</A
></H3
><P
>     While the standard syntax for specifying string constants is usually
     convenient, it can be difficult to understand when the desired string
     contains many single quotes or backslashes, since each of those must
     be doubled. To allow more readable queries in such situations,
     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> provides another way, called
     <SPAN
CLASS="QUOTE"
>"dollar quoting"</SPAN
>, to write string constants.
     A dollar-quoted string constant
     consists of a dollar sign (<TT
CLASS="LITERAL"
>$</TT
>), an optional
     <SPAN
CLASS="QUOTE"
>"tag"</SPAN
> of zero or more characters, another dollar
     sign, an arbitrary sequence of characters that makes up the
     string content, a dollar sign, the same tag that began this
     dollar quote, and a dollar sign. For example, here are two
     different ways to specify the string <SPAN
CLASS="QUOTE"
>"Dianne's horse"</SPAN
>
     using dollar quoting:
</P><PRE
CLASS="PROGRAMLISTING"
>$$Dianne's horse$$
$SomeTag$Dianne's horse$SomeTag$</PRE
><P>
     Notice that inside the dollar-quoted string, single quotes can be
     used without needing to be escaped.  Indeed, no characters inside
     a dollar-quoted string are ever escaped: the string content is always
     written literally.  Backslashes are not special, and neither are
     dollar signs, unless they are part of a sequence matching the opening
     tag.
    </P
><P
>     It is possible to nest dollar-quoted string constants by choosing
     different tags at each nesting level.  This is most commonly used in
     writing function definitions.  For example:
</P><PRE
CLASS="PROGRAMLISTING"
>$function$
BEGIN
    RETURN ($1 ~ $q$[\t\r\n\v\\]$q$);
END;
$function$</PRE
><P>
     Here, the sequence <TT
CLASS="LITERAL"
>$q$[\t\r\n\v\\]$q$</TT
> represents a
     dollar-quoted literal string <TT
CLASS="LITERAL"
>[\t\r\n\v\\]</TT
>, which will
     be recognized when the function body is executed by
     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.  But since the sequence does not match
     the outer dollar quoting delimiter <TT
CLASS="LITERAL"
>$function$</TT
>, it is
     just some more characters within the constant so far as the outer
     string is concerned.
    </P
><P
>     The tag, if any, of a dollar-quoted string follows the same rules
     as an unquoted identifier, except that it cannot contain a dollar sign.
     Tags are case sensitive, so <TT
CLASS="LITERAL"
>$tag$String content$tag$</TT
>
     is correct, but <TT
CLASS="LITERAL"
>$TAG$String content$tag$</TT
> is not.
    </P
><P
>     A dollar-quoted string that follows a keyword or identifier must
     be separated from it by whitespace; otherwise the dollar quoting
     delimiter would be taken as part of the preceding identifier.
    </P
><P
>     Dollar quoting is not part of the SQL standard, but it is often a more
     convenient way to write complicated string literals than the
     standard-compliant single quote syntax.  It is particularly useful when
     representing string constants inside other constants, as is often needed
     in procedural function definitions.  With single-quote syntax, each
     backslash in the above example would have to be written as four
     backslashes, which would be reduced to two backslashes in parsing the
     original string constant, and then to one when the inner string constant
     is re-parsed during function execution.
    </P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-BIT-STRINGS"
>4.1.2.5. Bit-string Constants</A
></H3
><P
>     Bit-string constants look like regular string constants with a
     <TT
CLASS="LITERAL"
>B</TT
> (upper or lower case) immediately before the
     opening quote (no intervening whitespace), e.g.,
     <TT
CLASS="LITERAL"
>B'1001'</TT
>.  The only characters allowed within
     bit-string constants are <TT
CLASS="LITERAL"
>0</TT
> and
     <TT
CLASS="LITERAL"
>1</TT
>.
    </P
><P
>     Alternatively, bit-string constants can be specified in hexadecimal
     notation, using a leading <TT
CLASS="LITERAL"
>X</TT
> (upper or lower case),
     e.g., <TT
CLASS="LITERAL"
>X'1FF'</TT
>.  This notation is equivalent to
     a bit-string constant with four binary digits for each hexadecimal digit.
    </P
><P
>     Both forms of bit-string constant can be continued
     across lines in the same way as regular string constants.
     Dollar quoting cannot be used in a bit-string constant.
    </P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="AEN1452"
>4.1.2.6. Numeric Constants</A
></H3
><P
>     Numeric constants are accepted in these general forms:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
>
<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
>.[<SPAN
CLASS="OPTIONAL"
><TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></SPAN
>][<SPAN
CLASS="OPTIONAL"
>e[<SPAN
CLASS="OPTIONAL"
>+-</SPAN
>]<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></SPAN
>]
[<SPAN
CLASS="OPTIONAL"
><TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></SPAN
>].<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
>[<SPAN
CLASS="OPTIONAL"
>e[<SPAN
CLASS="OPTIONAL"
>+-</SPAN
>]<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></SPAN
>]
<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
>e[<SPAN
CLASS="OPTIONAL"
>+-</SPAN
>]<TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
></PRE
><P>
     where <TT
CLASS="REPLACEABLE"
><I
>digits</I
></TT
> is one or more decimal
     digits (0 through 9).  At least one digit must be before or after the
     decimal point, if one is used.  At least one digit must follow the
     exponent marker (<TT
CLASS="LITERAL"
>e</TT
>), if one is present.
     There cannot be any spaces or other characters embedded in the
     constant.  Note that any leading plus or minus sign is not actually
     considered part of the constant; it is an operator applied to the
     constant.
    </P
><P
>     These are some examples of valid numeric constants:
<P
CLASS="LITERALLAYOUT"
>42<br>
3.5<br>
4.<br>
.001<br>
5e2<br>
1.925e-3</P
>
    </P
><P
>     
     
     
     A numeric constant that contains neither a decimal point nor an
     exponent is initially presumed to be type <TT
CLASS="TYPE"
>integer</TT
> if its
     value fits in type <TT
CLASS="TYPE"
>integer</TT
> (32 bits); otherwise it is
     presumed to be type <TT
CLASS="TYPE"
>bigint</TT
> if its
     value fits in type <TT
CLASS="TYPE"
>bigint</TT
> (64 bits); otherwise it is
     taken to be type <TT
CLASS="TYPE"
>numeric</TT
>.  Constants that contain decimal
     points and/or exponents are always initially presumed to be type
     <TT
CLASS="TYPE"
>numeric</TT
>.
    </P
><P
>     The initially assigned data type of a numeric constant is just a
     starting point for the type resolution algorithms.  In most cases
     the constant will be automatically coerced to the most
     appropriate type depending on context.  When necessary, you can
     force a numeric value to be interpreted as a specific data type
     by casting it.
     For example, you can force a numeric value to be treated as type
     <TT
CLASS="TYPE"
>real</TT
> (<TT
CLASS="TYPE"
>float4</TT
>) by writing:

</P><PRE
CLASS="PROGRAMLISTING"
>REAL '1.23'  -- string style
1.23::REAL   -- PostgreSQL (historical) style</PRE
><P>

     These are actually just special cases of the general casting
     notations discussed next.
    </P
></DIV
><DIV
CLASS="SECT3"
><H3
CLASS="SECT3"
><A
NAME="SQL-SYNTAX-CONSTANTS-GENERIC"
>4.1.2.7. Constants of Other Types</A
></H3
><P
>     A constant of an <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>arbitrary</I
></SPAN
> type can be
     entered using any one of the following notations:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'
'<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'::<TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
>
CAST ( '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>' AS <TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> )</PRE
><P>
     The string constant's text is passed to the input conversion
     routine for the type called <TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
>. The
     result is a constant of the indicated type.  The explicit type
     cast can be omitted if there is no ambiguity as to the type the
     constant must be (for example, when it is assigned directly to a
     table column), in which case it is automatically coerced.
    </P
><P
>     The string constant can be written using either regular SQL
     notation or dollar-quoting.
    </P
><P
>     It is also possible to specify a type coercion using a function-like
     syntax:
</P><PRE
CLASS="SYNOPSIS"
><TT
CLASS="REPLACEABLE"
><I
>typename</I
></TT
> ( '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>' )</PRE
><P>
     but not all type names can be used in this way; see <A
HREF="sql-expressions.html#SQL-SYNTAX-TYPE-CASTS"
>Section 4.2.9</A
> for details.
    </P
><P
>     The <TT
CLASS="LITERAL"
>::</TT
>, <TT
CLASS="LITERAL"
>CAST()</TT
>, and
     function-call syntaxes can also be used to specify run-time type
     conversions of arbitrary expressions, as discussed in <A
HREF="sql-expressions.html#SQL-SYNTAX-TYPE-CASTS"
>Section 4.2.9</A
>.  To avoid syntactic ambiguity, the
     <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'</TT
>
     syntax can only be used to specify the type of a simple literal constant.
     Another restriction on the
     <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'</TT
>
     syntax is that it does not work for array types; use <TT
CLASS="LITERAL"
>::</TT
>
     or <TT
CLASS="LITERAL"
>CAST()</TT
> to specify the type of an array constant.
    </P
><P
>     The <TT
CLASS="LITERAL"
>CAST()</TT
> syntax conforms to SQL.  The
     <TT
CLASS="LITERAL"
><TT
CLASS="REPLACEABLE"
><I
>type</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>'</TT
>
     syntax is a generalization of the standard: SQL specifies this syntax only
     for a few data types, but <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> allows it
     for all types.  The syntax with
     <TT
CLASS="LITERAL"
>::</TT
> is historical <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
     usage, as is the function-call syntax.
    </P
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-OPERATORS"
>4.1.3. Operators</A
></H2
><P
>    An operator name is a sequence of up to <TT
CLASS="SYMBOL"
>NAMEDATALEN</TT
>-1
    (63 by default) characters from the following list:
<P
CLASS="LITERALLAYOUT"
>+&nbsp;-&nbsp;*&nbsp;/&nbsp;&lt;&nbsp;&gt;&nbsp;=&nbsp;~&nbsp;!&nbsp;@&nbsp;#&nbsp;%&nbsp;^&nbsp;&amp;&nbsp;|&nbsp;`&nbsp;?</P
>

    There are a few restrictions on operator names, however:
    <P
></P
></P><UL
><LI
><P
>       <TT
CLASS="LITERAL"
>--</TT
> and <TT
CLASS="LITERAL"
>/*</TT
> cannot appear
       anywhere in an operator name, since they will be taken as the
       start of a comment.
      </P
></LI
><LI
><P
>       A multiple-character operator name cannot end in <TT
CLASS="LITERAL"
>+</TT
> or <TT
CLASS="LITERAL"
>-</TT
>,
       unless the name also contains at least one of these characters:
<P
CLASS="LITERALLAYOUT"
>~&nbsp;!&nbsp;@&nbsp;#&nbsp;%&nbsp;^&nbsp;&amp;&nbsp;|&nbsp;`&nbsp;?</P
>
       For example, <TT
CLASS="LITERAL"
>@-</TT
> is an allowed operator name,
       but <TT
CLASS="LITERAL"
>*-</TT
> is not.  This restriction allows
       <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> to parse SQL-compliant
       queries without requiring spaces between tokens.
      </P
></LI
></UL
><P>
   </P
><P
>    When working with non-SQL-standard operator names, you will usually
    need to separate adjacent operators with spaces to avoid ambiguity.
    For example, if you have defined a left unary operator named <TT
CLASS="LITERAL"
>@</TT
>,
    you cannot write <TT
CLASS="LITERAL"
>X*@Y</TT
>; you must write
    <TT
CLASS="LITERAL"
>X* @Y</TT
> to ensure that
    <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> reads it as two operator names
    not one.
   </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN1565"
>4.1.4. Special Characters</A
></H2
><P
>   Some characters that are not alphanumeric have a special meaning
   that is different from being an operator.  Details on the usage can
   be found at the location where the respective syntax element is
   described.  This section only exists to advise the existence and
   summarize the purposes of these characters.

   <P
></P
></P><UL
><LI
><P
>      A dollar sign (<TT
CLASS="LITERAL"
>$</TT
>) followed by digits is used
      to represent a positional parameter in the body of a function
      definition or a prepared statement.  In other contexts the
      dollar sign can be part of an identifier or a dollar-quoted string
      constant.
     </P
></LI
><LI
><P
>      Parentheses (<TT
CLASS="LITERAL"
>()</TT
>) have their usual meaning to
      group expressions and enforce precedence.  In some cases
      parentheses are required as part of the fixed syntax of a
      particular SQL command.
     </P
></LI
><LI
><P
>      Brackets (<TT
CLASS="LITERAL"
>[]</TT
>) are used to select the elements
      of an array.  See <A
HREF="arrays.html"
>Section 8.14</A
> for more information
      on arrays.
     </P
></LI
><LI
><P
>      Commas (<TT
CLASS="LITERAL"
>,</TT
>) are used in some syntactical
      constructs to separate the elements of a list.
     </P
></LI
><LI
><P
>      The semicolon (<TT
CLASS="LITERAL"
>;</TT
>) terminates an SQL command.
      It cannot appear anywhere within a command, except within a
      string constant or quoted identifier.
     </P
></LI
><LI
><P
>      The colon (<TT
CLASS="LITERAL"
>:</TT
>) is used to select
      <SPAN
CLASS="QUOTE"
>"slices"</SPAN
> from arrays. (See <A
HREF="arrays.html"
>Section 8.14</A
>.)  In certain SQL dialects (such as Embedded
      SQL), the colon is used to prefix variable names.
     </P
></LI
><LI
><P
>      The asterisk (<TT
CLASS="LITERAL"
>*</TT
>) is used in some contexts to denote
      all the fields of a table row or composite value.  It also
      has a special meaning when used as the argument of an
      aggregate function, namely that the aggregate does not require
      any explicit parameter.
     </P
></LI
><LI
><P
>      The period (<TT
CLASS="LITERAL"
>.</TT
>) is used in numeric
      constants, and to separate schema, table, and column names.
     </P
></LI
></UL
><P>

   </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-SYNTAX-COMMENTS"
>4.1.5. Comments</A
></H2
><P
>    A comment is a sequence of characters beginning with
    double dashes and extending to the end of the line, e.g.:
</P><PRE
CLASS="PROGRAMLISTING"
>-- This is a standard SQL comment</PRE
><P>
   </P
><P
>    Alternatively, C-style block comments can be used:
</P><PRE
CLASS="PROGRAMLISTING"
>/* multiline comment
 * with nesting: /* nested block comment */
 */</PRE
><P>
    where the comment begins with <TT
CLASS="LITERAL"
>/*</TT
> and extends to
    the matching occurrence of <TT
CLASS="LITERAL"
>*/</TT
>. These block
    comments nest, as specified in the SQL standard but unlike C, so that one can
    comment out larger blocks of code that might contain existing block
    comments.
   </P
><P
>    A comment is removed from the input stream before further syntax
    analysis and is effectively replaced by whitespace.
   </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SQL-PRECEDENCE"
>4.1.6. Operator Precedence</A
></H2
><P
>    <A
HREF="sql-syntax-lexical.html#SQL-PRECEDENCE-TABLE"
>Table 4-2</A
> shows the precedence and
    associativity of the operators in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>.
    Most operators have the same precedence and are left-associative.
    The precedence and associativity of the operators is hard-wired
    into the parser.  This can lead to non-intuitive behavior; for
    example the Boolean operators <TT
CLASS="LITERAL"
>&lt;</TT
> and
    <TT
CLASS="LITERAL"
>&gt;</TT
> have a different precedence than the Boolean
    operators <TT
CLASS="LITERAL"
>&lt;=</TT
> and <TT
CLASS="LITERAL"
>&gt;=</TT
>.  Also, you will
    sometimes need to add parentheses when using combinations of
    binary and unary operators.  For instance:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 5 ! - 6;</PRE
><P>
   will be parsed as:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 5 ! (- 6);</PRE
><P>
    because the parser has no idea &mdash; until it is too late
    &mdash; that <TT
CLASS="TOKEN"
>!</TT
> is defined as a postfix operator,
    not an infix one.  To get the desired behavior in this case, you
    must write:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT (5 !) - 6;</PRE
><P>
    This is the price one pays for extensibility.
   </P
><DIV
CLASS="TABLE"
><A
NAME="SQL-PRECEDENCE-TABLE"
></A
><P
><B
>Table 4-2. Operator Precedence (decreasing)</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>Operator/Element</TH
><TH
>Associativity</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="TOKEN"
>.</TT
></TD
><TD
>left</TD
><TD
>table/column name separator</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>::</TT
></TD
><TD
>left</TD
><TD
><SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>-style typecast</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>[</TT
> <TT
CLASS="TOKEN"
>]</TT
></TD
><TD
>left</TD
><TD
>array element selection</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>+</TT
> <TT
CLASS="TOKEN"
>-</TT
></TD
><TD
>right</TD
><TD
>unary plus, unary minus</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>^</TT
></TD
><TD
>left</TD
><TD
>exponentiation</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>*</TT
> <TT
CLASS="TOKEN"
>/</TT
> <TT
CLASS="TOKEN"
>%</TT
></TD
><TD
>left</TD
><TD
>multiplication, division, modulo</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>+</TT
> <TT
CLASS="TOKEN"
>-</TT
></TD
><TD
>left</TD
><TD
>addition, subtraction</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>IS</TT
></TD
><TD
>&nbsp;</TD
><TD
><TT
CLASS="LITERAL"
>IS TRUE</TT
>, <TT
CLASS="LITERAL"
>IS FALSE</TT
>, <TT
CLASS="LITERAL"
>IS NULL</TT
>, etc</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>ISNULL</TT
></TD
><TD
>&nbsp;</TD
><TD
>test for null</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>NOTNULL</TT
></TD
><TD
>&nbsp;</TD
><TD
>test for not null</TD
></TR
><TR
><TD
>(any other)</TD
><TD
>left</TD
><TD
>all other native and user-defined operators</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>IN</TT
></TD
><TD
>&nbsp;</TD
><TD
>set membership</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>BETWEEN</TT
></TD
><TD
>&nbsp;</TD
><TD
>range containment</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>OVERLAPS</TT
></TD
><TD
>&nbsp;</TD
><TD
>time interval overlap</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>LIKE</TT
> <TT
CLASS="TOKEN"
>ILIKE</TT
> <TT
CLASS="TOKEN"
>SIMILAR</TT
></TD
><TD
>&nbsp;</TD
><TD
>string pattern matching</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>&lt;</TT
> <TT
CLASS="TOKEN"
>&gt;</TT
></TD
><TD
>&nbsp;</TD
><TD
>less than, greater than</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>=</TT
></TD
><TD
>right</TD
><TD
>equality, assignment</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>NOT</TT
></TD
><TD
>right</TD
><TD
>logical negation</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>AND</TT
></TD
><TD
>left</TD
><TD
>logical conjunction</TD
></TR
><TR
><TD
><TT
CLASS="TOKEN"
>OR</TT
></TD
><TD
>left</TD
><TD
>logical disjunction</TD
></TR
></TBODY
></TABLE
></DIV
><P
>    Note that the operator precedence rules also apply to user-defined
    operators that have the same names as the built-in operators
    mentioned above.  For example, if you define a
    <SPAN
CLASS="QUOTE"
>"+"</SPAN
> operator for some custom data type it will have
    the same precedence as the built-in <SPAN
CLASS="QUOTE"
>"+"</SPAN
> operator, no
    matter what yours does.
   </P
><P
>    When a schema-qualified operator name is used in the
    <TT
CLASS="LITERAL"
>OPERATOR</TT
> syntax, as for example in:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT 3 OPERATOR(pg_catalog.+) 4;</PRE
><P>
    the <TT
CLASS="LITERAL"
>OPERATOR</TT
> construct is taken to have the default precedence
    shown in <A
HREF="sql-syntax-lexical.html#SQL-PRECEDENCE-TABLE"
>Table 4-2</A
> for <SPAN
CLASS="QUOTE"
>"any other"</SPAN
> operator.  This is true no matter
    which specific operator appears inside <TT
CLASS="LITERAL"
>OPERATOR()</TT
>.
   </P
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